Proctor Christine M, Freeman Elizabeth W, Brown Janine L
Department of Reproductive Sciences, Smithsonian National Zoological Park, Conservation and Research Center, Front Royal, Virginia 22630, USA.
Zoo Biol. 2010 Mar-Apr;29(2):168-78. doi: 10.1002/zoo.20292.
The North American African (Loxodonta africana) elephant population is not self-sustaining, in part because of a high rate of abnormal ovarian activity. About 12% of adult females exhibit irregular cycles and 31% do not cycle at all. Our earlier work revealed a relationship between dominance status and ovarian acyclicity, with dominant females being more likely to not cycle normally. One theory is that dominant females may be expending more energy to maintaining peace within the captive herd than for supporting reproduction. The goal of this study was to determine if there was a relationship among dominance status, serum cortisol concentrations, and ovarian acyclicity. We hypothesized that adrenal glucocorticoid activity would be increased in dominant, noncycling elephants as compared with subdominant individuals. Blood samples were collected weekly over a 2-year period in 81 females of known dominance and cyclicity status, and analyzed for cortisol. Based on a path analysis model (Reticular Action Model Or Near Approximation [RAMONA]), noncycling, dominant African elephant females did not have higher mean serum cortisol concentrations, or exhibit more variability (i.e., coefficient of variation, standard deviation) in cortisol secretion. This study suggests that alterations in adrenal activity are not related to dominance status nor contribute directly to acyclicity in captive African elephants.
北美非洲象（非洲象属）种群无法自我维持，部分原因是卵巢活动异常率较高。约12%的成年雌性表现出不规律的周期，31%根本不发情。我们早期的研究揭示了优势地位与卵巢无周期性之间的关系，优势雌性更有可能无法正常发情。一种理论认为，优势雌性可能在维持圈养象群内部和平上消耗了更多能量，而非用于支持繁殖。本研究的目的是确定优势地位、血清皮质醇浓度和卵巢无周期性之间是否存在关联。我们假设，与从属个体相比，处于优势地位、不发情的大象的肾上腺糖皮质激素活性会增加。在两年时间里，每周采集81头已知优势地位和发情状态的雌性大象的血样，并分析其中的皮质醇。基于路径分析模型（网状作用模型或近似模型[RAMONA]），处于优势地位、不发情的非洲象雌性的平均血清皮质醇浓度并不更高，皮质醇分泌的变异性（即变异系数、标准差）也没有更大。本研究表明，肾上腺活动的改变与优势地位无关，也不会直接导致圈养非洲象出现无周期性发情。
